Control means for liquid-operated servo-mechanisms



Dec. 20, 1955 HARR|5 2,727,525

CONTROL. MEANS FOR LIQUID-OPERATED SERVO-MECHANISMS Filed July 22, 1952 Lu) elm-2:01 T12 ,H @191 L6 CONTROL MEANS FOR LIQUID-OPERATED SERVO-MECHANISMS Thomas Alfred Harris, Edgbaston, Birmingham, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Application July 22, 1952, Serial No. 300,175 .Claims priority, application Great Britain July 30, 1951 2 Claims. (Cl. 137-83) For the control of a liquid operated servo-mechanism, and particularly a servo-mechanism used for controlling the rate of supply of liquid fuel to a jet-engine, or gas turbine, it is known to employ a device of the kind comprising a liquid duct formed by a pair of coaxial passages having a gap between their adjacent ends, for conveying the motive liquid of the servo mechanism. These passages are contained in a chamber having a freely-open vent or'discharge outlet. In this chamber there has hitherto been mounted a shutter movable across the gap between the passages and responsive to any desired condition, such as the variable pressure of liquid fuel on a diaphragm or piston, to which the shutter is connected, the rate at which motive liquid is supplied across the gap to a part of the servo-mechanism being determined by the shutter.

The object of the present invention is to provide other means in a device of the kind aforesaid for acting on the liquid flowing across the gap.

The invention comprises the combination with a pair of coaxial passages having a gap between their adjacent ends for conveying the motive liquid of the servo-mechanism, of at least one nozzle adapted to direct a control jet of liquid transversely across the gap, and a valve responsive to a particular condition for controlling the flow to the nozzle.

The accompanying diagram illustrates one embodiment of the invention.

In carrying the invention into effect in the manner shown in the diagram, a pair of coaxial passages a having a gap between their adjacent ends, are contained in a chamber b having an outlet. These passages a serve, as hitherto, for conveying the motive liquid of the servomechanism. At opposite sides of the gap there are mounted a pair of nozzles e adapted to direct a jet of control liquid under pressure across the gap and so divert some or all of the motive liquid from one of the passages connected to the servo-mechanism.

In the example shown, one of the nozzles is controlled by a spring loaded valve 1 responsive to a particular predetermined liquid pressure related to the speed of a pump. The other nozzle is controlled by a spring loaded valve g which is movable to its open position by an electromagnet h, the latter receiving current from one or more thermocouples i through an amplifier j.

In another arrangement, a mounted around the gap, by a valve responsive to a The motive liquid may or any other source.

The system shown in the diagram is for supplying liquid fuel to a burner k in the combustion chamber of a jetengine or gas turbine. The fuel pump is of the kind comprising a hollow housing d enclosing a rotor m in which are formed a plurality of bores. In each bore is contained a spring-loaded plunger n which at its outer end abuts against an adjustable swash plate 0. The inlet of the pump is indicated by c and the outlet by p. For

plurality of nozzles are each nozzle being controlled particular condition.

be derived from a fuel pump,

elfecting angular adjustment of the swash plate, there is incorporated with the pump housing a cylinder q of the servo mechanism, and in the cylinder is contained a piston r which is movable in one direction by a spring s. A rod t extending from the piston is attached to the swash plate. The two ends of the to a control means as above described by pipes comuwith the pump outlet p. In the rotor is formed a radial passage v which at one end communicates with the pump inlet 0. When the rotor m is in motion liquid is discharged from the passage v into the housing at a pressure related to the speed of the rotor, and this pressure is utilised to actuate the valve 1 through a piston w contained in a cylinder x which at one end is in communication with the pump housing, the other end being in communication with the pump inlet by way of a pipe y. So long as the valve 1 remains closed, equal liquid pressures act on the opposite sides of the servo piston r and the latter is held at the left hand end of the cylinder by the associated spring s as shown, so causing the swash in the position at which maximum delivery is given by the pump. Liquid supplied by the pump to the chamber 1; of the servo control means is returned to the pump inlet by the pipe 2, the jet flowing is sufiicient to open the valve f, the liquid supplied by the pump flows through the passage 3 and the valve, and thence through a pipe 5 to one of the nozzles e. This causes the jet of the servo control means to be deflected laterally with consequent reduction of the liquid pressure in the right hand end of the servo cylinder q. The preponderating liquid pressure in the left hand end of this cylinder then moves the piston r to the right against the action of the spring s, causing the swash plate 0 to be moved in the direction for reducing the pump output.

In the system illustrated the servo control means is also responsive (as already mentioned) to the action of liquid flowing through the other nozzle e under the control of the valve g which is supplied with liquid from the pump along the pipe 6. The valve is under the control of one or more thermo couples i located in the comperature is exceeded. If desired additional nozzles may be arranged around the gap between the ends of the passages a and supplied with liquid under the control of valves responsive to other conditions than those specified.

The use of the invention is not, however, restricted to the use in such a system as that illustrated by the diagram, as it may be applied to other analogous uses. Thus it may be applied to a fuel supply system in which a constant output pump is used, the quantity of fuel supplied to the burner being varied under the control of a servo-mechanism which actuates a by-pass valve through which a part of the fuel supplied by the pump is returned to the pump or a supply tank. Moreover the servo-mechanism shown in the drawing could alternatively be used for actuating a throttle in the fuel supply line, or other means for regulating the rate of supply of fuel to the burner.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. Control means for a liquid operated servo-mechanism, comprising in combination with the servo-mechanism, a pair of coaxial passages through which motive liquid employed for actuating the servo-mechanism can flow, and which have adjacent ends separated by a gap,

a fixed nozzle situated adjacent to the gap and arranged to direct a jet of liquid transversely across the gap for diverting from one of the passages some or all of the motive liquid issuing from the other passage, and an automatically operable valve for controlling the supply of liquid to the nozzle.

2. Control means for a liquid operated servo-mechanism comprising in combination with the servo-mechanism, a pair of coaxial passages through which motive liquid employed for actuating the servo-mechanism can 10 flow, and which have adjacent ends separated by a gap, a plurality of fixed nozzles situated adjacent to the gap and arranged to direct jets of liquid transversely across the gap for diverting from one of the passages some or all of the liquid issuing from the other passage, and automatically operable valves for controlling the supply of liquid to the nozzles.

References Cited in the tile of this patent UNITED STATES PATENTS Rosch Oct. 26, 1943 Braithwaite et al Oct. 1, 1946 Todd Oct. 1, 1946 FOREIGN PATENTS France Oct. 7, 1929 Germany Nov. 7, 1932 

